Magnetic head and producing method of the same

Abstract: A magnetic head can be made by: a first step of butting projection end faces of a pair of magnetic cores (11,12) each of which is previously machined into a convex shape, through a magnetic gap member (1); a second step of forming notches (14a,14b) which reach a winding groove (21), at said butted projection end faces of said magnetic cores by an electric discharge machining process, thereby regulating a track width (Tw); and a third step of filling under heat treatment glass (15,16) into grooves (17a,18a) at two sides of said pair of convex magnetic cores and said notches . When the magnetic head is used, a magnetic recording/reproduction apparatus which is suitable for high density recording such as a digital VTR is provided.

Description: Background of the Invention 1. Field of the Invention The invention relates to a magnetic head as set forth in the preamble of claim 1 and to a method of manufacturing a magnetic head as set forth in the preamble of claim 5. A magnetic head and a method of this kind are known from US-A-4 425 701. The aforementioned document discloses a method in which by separate cutting or dicing steps two comb-like structures are formed from ferromagnetic substance core blocks, said dicing steps forming partial grooves which are separated from one other by a tooth or projection. After having filled the partial grooves with glass, mirror-grinded the blocks including the end faces of the projections and applied a gap spacer or film, the blocks are abutted to one another in a manner that opposing end faces of the projections of the opposing blocks match. After bonding the blocks to one another, the assembly thus formed is cut into the individual heads. There is no other grinding or cutting process which could influence the track width of the magnetic gap defined by the width of the projections. The accuracy of the track width of the magnetic gap is dependent of the accuracy with which the blocks are aligned. A mis-alignment influences the accuracy of the track width of all magnetic gaps. Further, the accuracy of the track width also depends of the accuracy of the width of the grooves. If those are unequal, it is not possible to attain an overall accuracy even if some of the track widths are accurately adjusted. All this is the result of the fact that an adjustment of the track width of the heads is not separately made. In a system such as a digital VTR wherein a large amount of signals are recorded and reproduced, it is essential to employ high density magnetic recording/reproduction techniques such as the narrow-track technique and the short-wavelength technique. Generally, it is known that high density recording/reproduction can be attained when the coercive force of a magnetic medium is increased and the saturation magnetic flux density (hereinafter referred to as "Bs") of a magnetic head is increased. Ferrit material which has mainly been used in the prior art as a magnetic head material has Bs of about 0.5 T. When a ferrite magnetic head is used for a metal tape having a coercive force as high as 80 kA/m or more, therefore, there occurs magnetic saturation so that recording cannot be conducted satisfactorily. To comply with this, researches have vigorously been conducted on magnetic heads using a material which has Bs larger than ferrite, such as a Sendust alloy material (Bs: about 1.0 T), a Co amorphous film (Bs: about 0.8 to 1.1 T), or a novel material such as a Co superstructure nitriding alloy film having Bs of 1.3 T or more, an Fe superstructure nitride film, or an Fe nitride film, particularly on a composite magnetic head or so-called MIG head in which the main core is made of ferrite and a magnetic thin film is disposed at least in the vicinity of the front gap. Fig. 10 shows the configuration of a MIG head. A pair of convex magnetic cores 2 and 3 which are opposed to each other through a magnetic gap 1 respectively comprise convex core bodies 4 and 5 made of ferrite, and high saturation magnetic flux density films 6 and 7 which cover the respective projection end faces of the core bodies and both the side faces elongating therefrom. The two magnetic cores 2 and 3 are coupled to each other by a pair of glass blocks 8 and 9 which are disposed at their both sides. The reference numeral 10 designates a winding hole through which coils can pass. In such a magnetic head, as shown in Fig. 11 in detail, track dis-adjustments d 1 and d 2 are easily produced by production errors due to machining accuracy of track grooves 4a and 5a of the pair of core bodies 4 and 5, and butting accuracy of the core bodies 4 and 5. Moreover, the presence of rounds 2a, 2b, 3a and 3b of edge portions of the magnetic films 6 and 7 further impairs the track width accuracy. In high density recording, these divergences and rounds of the edges tend to cause the properties to be impaired. As partly disclosed by U.S. Pat. No. 4,110,902, a method of regulating the track width by using a wire on a sliding face may be employed. In the method, however, the whole of the sliding face is machined so as to have a fixed track width, and the running of a magnetic medium causes a problem of abrasion resistance. Furthermore, magnetic properties are greatly impaired. According to the invention, a machining process is conducted only on the vicinity of a gap, and therefore the problem of abrasion resistance and the impairment of magnetic properties do not occur. U.S. Pat. No. 3,668,775 discloses a configuration in which the whole of a core constitutes the track width. Also in this configuration, magnetic properties are greatly impaired. Moreover, the chip has a reduced strength. U.S. Pat. No. 5,208,965 discloses a method in which a track width is regulated by track width regulation grooves. In the disclosed method, cores are separately machined, and then butted to be joined to each other, thereby producing butting errors. Therefore, the method cannot be employed in a production of a narrow-track width head. Recently, the track width and its accuracy are requested to be 10 µm or less and ±0.5 µm, respectively. As described above, however, it is substantially impossible according to the prior art to produce a magnetic head which fulfills the requirements while preventing the magnetic properties from being impaired. SUMMARY OF THE INVENTION It is an object of the invention to provide a narrow-track magnetic head for high density recording and of high performance. It is another object of the invention to provide a method of producing a narrow-track magnetic head at an improved yield and a lower cost. It is a further object of the invention to provide a magnetic recording/reproduction apparatus which is suitable for a narrow track pitch. The above objects are attained by the process and apparatus defined in the appended claims. According to the process and the head configuration defined in the appended claims, a magnetic head which is suitable for a narrow track used in high density recording and free from a track divergence can be obtained at an improved yield and a lower cost. Since the track width is constant over a range from the face to the winding groove, furthermore, the track width does not vary even when the magnetic head is abraded, so that a head of high reliability is supplied. When the head is used, it is possible to provide a magnetic recording/reproduction apparatus which is suitable for a digital VTR. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a magnetic head chip of an embodiment of the invention; Fig. 2 is a plan view of a part of the magnetic head chip of the embodiment of the invention; Fig. 3 is a perspective view illustrating a production method of an embodiment of the invention; Fig. 4 is a perspective view illustrating the production method of the embodiment of the invention; Fig. 5 is a perspective view illustrating the production method of the embodiment of the invention; Fig. 6 is a perspective view illustrating the production method of the embodiment of the invention; Fig. 7 is a perspective view illustrating the production method of the embodiment of the invention; Fig. 8 is a perspective view illustrating a production method of another embodiment of the invention; Fig. 9 is a perspective view illustrating a magnetic head and its vicinity of a magnetic recording apparatus of the invention; Fig. 10 is a perspective view of a prior art magnetic head chip; and Fig. 11 is a plan view of a part of the prior art magnetic head chip. DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the invention will be described with reference to the drawings. A magnetic head shown in Figs. 1 and 2 is fundamentally different from the prior art magnetic head shown in Figs. 10 and 12 in that a pair of convex magnetic cores 11 and 12 have notches 13a and 14a which dig into side faces of magnetic films 19 and 20 in the range from the magnetic tape sliding face of the cores to a winding window 21 and are cut to an equal size in a direction perpendicular to the track width direction, and that the track width TW is regulated by the notches 13a and 14a. In the magnetic head, the pair of convex magnetic cores 11 and 12 which are opposed to each other through a magnetic gap 1 are bonded to each other by glass blocks 15 and 16. The convex magnetic cores 11 and 12 are mainly made of ferrite, and have the magnetic films 19 and 20 and the convex core bodies 17,18 . The magnetic films 19,20 have a high saturation magnetic flux density and cover the respective projection end faces of the convex core bodies 17 and 18 and both the side faces elongating therefrom. The side faces of the magnetic films 19 and 20 are cut to an equal size in the track width direction by the notches 13a and 14a. The notches reach the winding groove 21 while maintaining the track width TW attained at the magnetic tape sliding face. The reference numerals 17a and 18a designate track grooves. The provision of the notches 13a and 14a eliminates the butting misalignment of the convex core bodies 17 and 18, and the influences of rounds of edges of the magnetic films 19 and 20. The track width TW depends on the distance between the notches 13a and 14a. Therefore, the track width TW can be regulated with high accuracy. Since the track width TW is constant over the range from the face to the winding groove 21, furthermore, the track width TW does not vary even when the head is abraded, so that a head of high reliability is supplied. As a material of the magnetic films 19 and 20, useful is a Sendust alloy material, a Co amorphous film, a Co superstructure nitriding alloy film, an Fe superstructure nitride film, an Fe nitride film, or the like. These materials may be disposed on the convex core bodies 17 and 18 by a suitable method such as vapor deposition, ion plating, or sputtering. The magnetic cores 11 and 12 are butted to each other through a gap member which is formed in the form of a film on at least one of the projection end faces of the cores. The gap member (which is not shown) may be made of a material such as SiO 2 , ZrO 2 , Ta 2 O 5 , glass, Cr, or a composite of these materials. When at least a part of the gap member is made of crystallized glass, the gap can be formed in a further satisfactory manner. The whole of the gap spacer may be made of crystallized glass. Crystallized glass is glass which, when it is again heated under special conditions after melting and shaping processes, is changed to an amorphous state and crystallized with preserving its original shape to have mechanical and thermal properties which are improved as compared with those of the original glass. Before the notches 13a and 14a are formed, the two magnetic cores 11 and 12 are firmly welded to each other. Therefore, the track width edges are prevented from being broken during the machining process, whereby the track width and the gap length can be formed stably. Preferably, the crystallized glass after the crystallization has the yield point higher than that of the glass blocks 15 and 16. When such glass is used, the gap portion is prevented from becoming loose in the process of forming the glass blocks 15 and 16, thereby allowing a gap to be formed in a further satisfactory manner. A method of producing the magnetic head will be described with reference to Figs. 3 to 8. First, a pair of substrates made of, for example, Mn-Zn ferrite and having a surface which is formed by a lapping process or the like so as to have excellent parallelism and smoothness are prepared. On the substrates, as shown in Fig. 3, parallel track grooves 17a and 18a for track regulation are formed by a grinding wheel or the like, thereby forming the pair of convex core bodies 17 and 18. At least one of the convex core bodies 17 and 18 is provided with the winding groove 21 through which coils can pass. As shown in Fig. 4, then, the magnetic films 19 and 20 which have a high saturation magnetic flux density are formed by a vacuum thin film forming technique so as to cover one side face of each of the core bodies 17 and 18, thereby completing the pair of magnetic cores 11 and 12. Next, a film-like gap member for forming the magnetic gap is disposed on one of the pair of magnetic cores 11 and 12. The magnetic cores 11 and 12 are arranged so as to oppose to each other through the gap member as shown in Fig. 5. The gap member (which is not shown) may be made of a material such as SiO 2 , ZrO 2 , Ta 2 O 5 , glass, Cr, or a composite of these materials. As shown in Fig. 6, a discharging electrode 25 is moved so as to approach the side portions of the pair of magnetic cores 11 and 12 in a butted state, to initiate a discharge, thereby forming notches 22. This allows the notches 22 to reach the winding groove 21 while maintaining the track width TW attained at the upper face. The butted state may be realized by supporting the cores by a jig, or by provisionally bonding the cores to each other by means of an adhesive. In order to further improve the gap accuracy, the following processes may be conducted. At least a part of the gap member, and the uppermost surface portions of the magnetic cores 11 and 12 are formed by crystallized glass. Then, the cores in the butted state are heated in an electric oven or the like so that the glass melt. The crystallized glass becomes amorphous to be crystallized, and has mechanical and thermal properties which are improved as compared with those of the original glass, with the result that the cores can firmly be bonded to each other at the gap portion. In place of crystallized glass, a metal such as At or Ag may be used so that the cores are heated and pressed to be diffusion-bonded. Alternatively, conventional glass having a low melting point may be used so that heating adhesion is conducted. In short, any method may be employed as far as it realizes means of making the gap faces contacted and bonded. As shown in Fig. 6, then, the discharging electrode 25 is moved so as to approach the side portions of the pair of magnetic cores 11 and 12 which are in a bonded state at the gap portion, to initiate a discharge, thereby forming the notches 22. In the process of forming the notches 22, since the magnetic cores 11 and 12 are already bonded to each other by the crystallized glass, phenomena such as the opening of the gap due to a machining load, the mixture of machining chips into the gap space, and the damage of the gap edges can be prevented from occurring, thereby remarkably improving the gap length accuracy and the track width accuracy. The surface roughness of the notches regulating the track width directly affects the track width accuracy. In order to attain the accuracy of ±0.5 µm, therefore, at least the surface roughness of 0.5 µm or less is required, and that of 0.2 µm or less is more preferable. In the case where the electric discharge machining was employed, when the single discharge energy was reduced to a level of 10 -7 J, a surface roughness of 0.1 to 0.2 µm was attained in the process of machining an Fe-Ta-N film. Generally, the electric discharge machining is conducted in insulating oil. Alternatively, pure water having an electrical resistivity of 1 MΩ·cm or higher may be used. When such water is used, a washing step in postprocesses may be omitted. As shown in Fig. 7, the pair of magnetic cores 11 and 12 are then coupled to each other by the glass blocks 15 and 16. The glass blocks 15 and 16 are formed by a filling process under heat treatment. Thereafter, the substrates are sliced into chips as indicated by one-dot chain lines, and coils are wound on each chip. According to the invention, the magnetic films 19 and 20 are formed also on the side faces of the core bodies 17 and 18 in the vicinity of the magnetic gap 1 which are directed to the magnetic gap, thereby realizing a configuration in which the MIG head can satisfactorily exhibit its advantages that saturation at the gap faces during a recording process is suppressed and that the recording ability is excellent. When the butting of the convex cores is previously conducted at a certain higher accuracy, the desired objects can be attained by conducting a discharge machining process only on a small portion of the magnetic films. In this case, the machining accuracy and speed are further improved. In the embodiment described above, the notches 22 are formed by a discharge machining process. Alternatively, the notches 22 may be formed by a laser induced etching process. In this alternative, as shown in Fig. 8, the pair of magnetic cores 11 and 12 in the butted state are irradiated from an upper side with an Ar laser beam 30 (having a spot diameter of 2 &Lm). During this process, the pair of magnetic cores 11 and 12 are immersed in a hydroxide of an alkali metal (for example, KOH), and therefore only a portion irradiated with the laser beam is machined by means of a thermal reaction. Preferably, the width Cw of the notches 22 in the longitudinal direction of the track is set to be 30 µm or less. The detail is shown in Fig. 2 (notches are designated by 13a and 14a). According to this configuration, the area to be machined can be reduced so that the machining speed is improved. In the invention, the machining of a notch of a width of 10 µm required a period of 10 sec. In this case, when the width Cw in the longitudinal direction of the track is 30 µm, the machining of both the notches 13a and 14a requires 60 sec. in total. This machining speed is equal to that for the track grooves 17a and 18a, and seemed as an upper limit for a mass production. When the portions of the magnetic films 19 and 20 for forming the notches 22 have a thickness of 3 µm or more, the machining accuracy is improved (when the film thickness is not greater than the spot diameter of the laser beam, the irradiation region becomes greater than the films so as to make the energy distribution nonuniform, thereby lowering the machining accuracy). The laser induced etching process is disclosed in Japanese laid open patent publication No. HEI2-276,009. The patent of the publication is directed to a process of machining a core block which is molded by glass, and is not related to a process of machining provisionally joined cores which have not yet been molded by glass as the case of the invention. In the invention, the approximate track regulating process is conducted by a grinding process before the laser induced etching process. As shown in Fig. 7, then, the pair of magnetic cores 11 and 12 are coupled to each other by the glass blocks 15 and 16. The glass blocks 15 and 16 are formed by a filling process under heat treatment. Thereafter, the substrates are sliced into chips as indicated by one-dot chain lines, and coils are wound on each chip. As described above, the invention is particularly effective in a narrow-gap and narrow-track MIG head. The invention can be applied also to a conventional ferrite head, and a head having a relatively large track width, and realizes an enhancement of the yield by means of improving the accuracy. The configuration in which the magnetic cores 11 and 12 are previously provided with the track grooves 17a and 18a as shown in Fig. 2 can reduce the machining amount of the notches 13a and 14a, and therefore is suitable for a mass production. Even when the track width Tw is small, furthermore, the configuration in which the track grooves 17a and 18a are respectively machined allows the core width Kw (Fig.2)to be large, so that a head which is excellent in chip strength and interface is provided. Fig. 9 shows an embodiment of the magnetic recording/reproduction apparatus of the invention. While running, a magnetic tape 34 makes contact with a magnetic head 32 mounted on a rotary cylinder 33 which conducts a helical scanning, and a signal is recorded on and reproduced from the magnetic tape 34. According to the invention, a head of a narrow track and free from a track divergence is used, and therefore magnetic fluxes are not blurred at track edges such as side fringes so that a very large amount of information is recorded and reproduced. Meawhile the material of the gap member can be non-crystallized glass .

Claims: A magnetic head comprising: a pair of magnetic cores (11, 12) each of which has a convex shape part (17, 18), said convex shape parts (17, 18) being opposed to each other through a magnetic gap member (1); a pair of glass blocks (15, 16) which are disposed at both sides of said magnetic cores (11, 12) to couple said magnetic cores (11, 12) to each other; and notches (13a, 14a) are formed at both sides of a magnetic tape sliding face constituted by upper faces of said convex shape parts (17, 18) of said magnetic cores (11, 12) to regulate a track width (TW), and said notches (13a, 14a) respectively reaching a winding groove (21) while maintaining the track width (TW), characterized in that said magnetic cores (11, 12) each are made of a composite of a core body (17, 18) mainly made of a ferrite and a metal magnetic film (19, 20), and said notches (13a, 14a) are formed only in the metal magnetic film (19, 20) after coupling said magnetic cores (11, 12) to each other. A magnetic head according to claim 1, wherein a width of said notches (13a, 14a) in a longitudinal direction of the track is 30 µm or less. A magnetic head according to one of claims 1 and 2, wherein at least a part of said magnetic gap member (1) is formed by crystallized glass. A method of manufacturing a magnetic head composed of a pair of magnetic cores each of which has a convex shape part, said convex shape parts being opposed to each other through a magnetic gap member, a pair of glass blocks which are disposed at both sides of said magnetic cores to couple said magnetic cores to each other, and notches formed at both sides of a magnetic tape sliding face constituted by upper faces of said convex shape parts of said magnetic cores to define a track width, said notches respectively reaching a winding groove while maintaining the track width, characterised in that after butting projection end faces of said magnetic cores through the magnetic gap member said notches are formed by an electric discharge machining process or by a laser induced etching process, to regulate the track width, and subsequent thereto glass is filled under heat treatment into said grooves and said notches at both sides of said magnetic cores. A method as set forth in claim 4 wherein said projection and faces are bonded to each other under the butted state by using at least a part of said magnetic gap member, before said notches are formed. A method of manufacturing a magnetic head according to claim 4 or 5, wherein said convex magnetic cores are made of a composite of a core body mainly made of a ferrite and a metal magnetic film, and said notches are formed only in said metal magnetic films. A method of manufacturing a magnetic head according to one of claims 4 to 6, wherein, in said process of forming notches which reach the winding groove by the electric discharge machining process, an insulation solvent for the electric discharge machining is water having an electrical resistivity of 1 MΩ·cm or higher. A method of manufacturing a magnetic head according to one of claims 5 and 6, wherein, in said process of forming notches which reach the winding groove by the laser induced etching process, portions of metal magnetic films for forming said notches have a thickness of 3 µm or more. A magnetic recording/reproduction apparatus comprising a magnetic head according to one of claims 1 to 3. A magnetic recording/reproduction apparatus comprising a magnetic head which is produced by a manufacturing method according to one of claims 4 to 8.

Inventors: HONMA YOSHIYASU, MASAKI KEN, TAKAHASHI KEN, HONMA, YOSHIYASU, MASAKI, KEN, TAKAHASHI, KEN
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1994
Main classification: G11B5
IPC codes: G11B5